Catalytic hydrogenation

ABSTRACT

The invention relates to a method for the catalytic hydrogenation of halogenated silanes or halogenated germanes, according to which halogenated monosilanes, oligosilanes or polysilanes, or monogermanes, oligogermanes or polygermanes, are hydrogenated or partially hydrogenated with hydrogenated Lewis acid-base pairs, and the partially halogenated Lewis acid base pairs can be rehydrogenated, especially with further addition of H 2  and the heterolysis thereof on the Lewis acid-base pairs, releasing hydrogen halide.

In accordance with the invention, a process is described for catalytic hydrogenation of halogenated silanes or germanes, in which halogenated mono-, oligo- or polysilanes or -germanes are hydrogenated or partially hydrogenated with hydrogenated Lewis acid-base pairs, and the partially halogenated Lewis acid-base pairs are hydrogenated again with release of hydrogen halide and more particularly with subsequent addition of H₂ and heterolysis thereof on the Lewis acid-base pairs.

The prior art discloses various processes for hydrogenating silanes and germanes. Halosilanes can be hydrogenated with metal hydrides, such as with titanium hydride according to, for example, SU 1766925 A1 or JP 50017035, with sodium hydride according to, for example, JP 2003313190 A2, with lithium hydride according to, for example, JP 1234316 or EP 102293 A2, with lithium aluminum hydride according to, for example, RU 2266293 C1 or U.S. Pat. No. 5,965,762 A or with sodium borohydride according to, for example, JP 2003119200 A2. The metal hydride may have organic substitution, as described, for example, in JP 61063515 A2 for diethylaluminum hydride. Halogenated oligosilanes can be partially hydrogenated by Si—Si bond cleavage with hydrogen halide in the presence of different catalysts, as disclosed, for example, in EP 737687 A1 or EP 574912 A1. SiCl₄ can be catalytically reacted with hydrogen to give HSiCl₃, for example according to U.S. Pat. No. 5,716,590. Even in the presence of a halide acceptor such as aluminum, magnesium or zinc metal, it is possible to react halosilanes with hydrogen, as described, for example, in U.S. Pat. No. 2,406,605, U.S. Pat. No. 5,329,038 A or DE 4119578 A1. SiH₄ can be obtained, for example according to JP 11156199 AA or JP 59121110 AA, by substituent exchange from HSiCl₃, which simultaneously forms SiCl₄.

Disadvantages of the known processes are firstly low yields and a large amount of by-products, and secondly the necessity of an electrochemical step for regeneration of the hydrogenating agent.

The prior art discloses, according to 1) G. C. Welch, R. R. S. Juan, J. D. Masuda, D. W. Stephan, “Reversible, metal-free hydrogen activation”, Science 2006, 314, 1124 and 2) G. C. Welch, D. W. Stephan, “Facile heterolytic cleavage of dihydrogen by phosphines and boranes”, J. Am. Chem. Soc. 2007, 129, 1880, that a combination of suitable phosphines PR₃ and boranes BR′₃ splits hydrogen heterolytically.

It is an object of the invention to provide a process for hydrogenating silicon halides or germanium halides, with which a particularly good yield can be achieved with a low proportion of by-products.

This object is achieved in accordance with the invention by a process according to claim 1.

Advantageous developments of the invention are described in the dependent claims.

The Lewis base used is preferably an R₃E where E=N, P or As and R=alkyl, aryl, O-alkyl, O-aryl or halogen, and the Lewis acid used is an R′₃E′ where E′=B, Al or Ga and where R′=alkyl, aryl, halogenated alkyl and aryl substituents or halogen.

The preferred elements of main group IV have been halogenated with chlorine or fluorine.

The Lewis acid-base pair is preferably hydrogenated at a temperature between −80° C. and 200° C. In addition, the Lewis acid-base pair is preferably hydrogenated at a pressure between 0.1 MPa and 10.0 MPa.

The hydrogenation of the halogenated silane/germane is preferably performed at a temperature between −20° C. and 200° C. In addition, the hydrogenation of the halogenated silane/germane is preferably performed at a pressure between 0.05 MPa and 0.5 MPa.

In a development of the process according to the invention, the element-hydrogen compounds of main group IV which precipitate out in solid form in a hydrogenation reactor are removed by means of a removal device at the base of the reactor. The element-hydrogen compounds of main group IV which outgas in the hydrogenation reactor are preferably obtained via a removal device.

The hydrogen halide which forms in a reaction reactor is preferably driven out thermally and withdrawn from the process via a valve. The hydrogen halide is preferably released at temperatures between 100° C. and 300° C.

In a specific embodiment of the process according to the invention, the second step is performed in a first reactor, and the third step in a second reactor. In this case, preference is given to feeding the regenerated Lewis acid-base pair back to the first reactor.

Appropriately, the halogenated Lewis acid-base pair is hydrogenated again in the third step by further addition of H₂.

The basis of the process according to the invention is the implementation of a catalyst system for catalytic conversion of monomeric, oligomeric or polymeric halosilanes to the corresponding hydrogenated polysilanes Si_(n)H_(n+2) and [SiH₂], by means of H₂. The same applies to the use of germanes.

The situation is also similar for mixtures of different halogenated silanes or germanes.

This catalytic conversion can be illustrated as follows:

The novel process includes, as well as the hydrogenation of halogenated oligo- or polysilanes, also the corresponding conversion of tetrachlorosilane or halogenated monosilanes to SiH₄.

The novel process for catalytic hydrogenation also enables partial hydrogenations, for example of SiCl₄ to HSiCl₃, in which case these partially hydrogenated products may in principle be sent to a further use or may be recycled into the process for full hydrogenation.

It is known from the prior art that Lewis acid-base pairs which cannot form direct adducts owing to their sterically hindered structure can serve as catalysts for heterolytic splitting of H₂. Lewis acid and Lewis base may be present as separate compounds, but they may also be present within one molecular compound. In addition, the catalytically active compounds may be fixed to support bodies.

The Lewis bases used may be compounds of the elements E=N, P or As, and the Lewis acids compounds of the elements E′=B, Al and Ga.

The novel catalytic cycle passes through, for example, the following circuit for hydrogenation of halogenated silanes

where R may be alkyl, aryl, O-alkyl, O-aryl or halogen, R′ may be alkyl, aryl, halogenated alkyl and aryl substituents or halogens, R*=H, halogen, alkyl, aryl, silyl, O-alkyl or O-aryl, and X═F, Cl, Br, I.

The process according to the invention proceeds essentially in three steps:

-   -   the heterolysis of H₂ (step 1) by the catalyst proceeds         preferably in the temperature range from −80° C. to 200° C. at         pressures of 0.1 MPa-10.0 MPa,     -   the hydrogenation of the halogen compounds (R*₃SiX) and the         removal of the hydrogenated products proceeds in a step 2         preferably at −20° C. to 200° C. and a pressure of 0.05-0.5 MPa,     -   in a third step the release of HX is performed thermally or         optionally with the aid of sterically very demanding and/or         non-nucleophilic bases. The thermal release is accomplished         preferably at 100° C. to 300° C.

In a first embodiment, the process according to the invention is illustrated in FIG. 1. In this embodiment, hydrogenation of the catalyst, conversion of the silane/germane and regeneration of the catalyst are performed in a single solvent or solvent mixture.

In a second embodiment, the process according to the invention is illustrated in FIG. 2. In this embodiment, the catalyst can be hydrogenated in a different solvent or solvent mixture than the conversion of the silane/germane, and the catalyst is isolated by distillation before the regeneration.

LIST OF REFERENCE NUMERALS

-   1. Connection to the hydrogenation reactor 4 -   2. Feed of halogenated silane or germane -   3. Removal of gaseous hydrogenated silanes and partially     hydrogenated halosilanes or halogermanes -   4. Hydrogenation reactor -   5. Gaseous hydrogenated silanes and partially hydrogenated     halosilanes or corresponding germanes -   6. Feed nozzle for halogenated silane or germane -   7. Reaction mixture in the hydrogenation reactor -   8. Precipitation of hydrogenated polysilanes or partially     hydrogenated halogenated polysilanes or corresponding germanes -   9. Removal stub -   10. Circulation pump -   11. Feed of spent Lewis acid-base pair to regeneration -   12. Regeneration reactor for driving out HX -   13. Heating coil -   14. Liquid level in the regeneration reactor -   15. Outlet stub for gaseous HX -   16. Outlet valve -   17. Gaseous HX -   18. Condenser -   19. Feed nozzle for H₂ -   20. Reaction mixture for heterolysis of H₂ -   21. Reactor for rehydrogenation of the Lewis acid-base pairs -   22. Feed valve for H₂ -   23. Feed of H₂ -   24. Removal stub for degassed catalyst -   25. Heating jacket -   26. Fill level of regeneration reactor -   27. Outlet stub for solvent vapor and gaseous HCl -   28. Outlet valve -   29. Gaseous solvent and/or HCl -   30. Removal stub for hydrogenated catalyst -   31. Feed for solvent and degassed catalyst -   32. Feed of solvent -   33. Feed for hydrogenated catalyst 

1. A process for hydrogenating silicon halides or germanium halides, characterized in that in a first step a Lewis acid-base pair is hydrogenated with addition of H₂, and in a second step monomeric, oligomeric or polymeric silicon halides or germanium halides are hydrogenated with an H⁻-containing Lewis acid-base pair, and in a third step the halogenated Lewis acid-base pair is regenerated with release of halogenated hydrogen.
 2. The process for hydrogenating silicon halides or germanium halides as claimed in claim 1, characterized in that the Lewis base used is an R₃E where E=N, P or As and R=alkyl, aryl, O-alkyl, O-aryl or halogen, and the Lewis acid used is an R′₃E′ where E′=B, Al or Ga and where R′=alkyl, aryl, halogenated alkyl and aryl substituents or halogen.
 3. The process for hydrogenating silicon halides or germanium halides as claimed in claim 1 or 2, characterized in that the preferred elements of main group IV are halogenated with chlorine or fluorine.
 4. The process for hydrogenating silicon halides and germanium halides as claimed in any of claims 1-3, characterized in that the hydrogenation of the Lewis acid-base pair is performed at a temperature between −80° C. and 200° C.
 5. The process for hydrogenating silicon halides and germanium halides as claimed in any of claims 1-4, characterized in that the hydrogenation of the Lewis acid-base pair is performed at a pressure between 0.1 MPa and 10.0 MPa.
 6. The process for hydrogenating silicon halides and germanium halides as claimed in any of claims 1-5, characterized in that the hydrogenation of the halogenated silane/germane is performed at a temperature between −20° C. and 200° C.
 7. The process for hydrogenating silicon halides and germanium halides as claimed in any of claims 1-6, characterized in that the hydrogenation of the halogenated silane/germane is performed at a pressure between 0.05 MPa and 0.5 MPa.
 8. The process for hydrogenating silicon halides and germanium halides as claimed in any of claims 1-7, characterized in that the element-hydrogen compounds of main group IV which precipitate out in solid form in a hydrogenation reactor (4) are removed by means of a removal device at the base of the reactor.
 9. The process for hydrogenating silicon halides and germanium halides as claimed in any of claims 1-8, characterized in that the element-hydrogen compounds of main group IV which outgas in a hydrogenation reactor (4) are obtained via a removal device.
 10. The process for hydrogenating silicon halides and germanium halides as claimed in any of claims 1-9, characterized in that hydrogen halide formed in a regeneration reactor (12) is driven out thermally and withdrawn from the process via a valve (16).
 11. The process for hydrogenating silicon halides and germanium halides as claimed in any of claims 1-10, characterized in that the hydrogen halide is released thermally at temperatures between 100° C. and 300° C.
 12. The process for hydrogenating silicon halides and germanium halides as claimed in any of the preceding claims, characterized in that the second step is performed in a first reactor and the third step in a second reactor.
 13. The process for hydrogenating silicon halides and germanium halides as claimed in claim 12, characterized in that the regenerated Lewis acid-base pair is fed back to the first reactor.
 14. The process for hydrogenating silicon halides and germanium halides as claimed in any of the preceding claims, characterized in that the halogenated Lewis acid-base pair is hydrogenated again in the third step with further addition of H₂. 